linux-kernel - Re: [PATCH] kvm: remove in_range from kvm_io

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Date:	Tue, 23 Jun 2009 12:14:00 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	avi@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	mtosatti@...hat.com, paulmck@...ux.vnet.ibm.com, markmc@...hat.com
Subject: Re: [PATCH] kvm: remove in_range from kvm_io_device

Michael S. Tsirkin wrote:
> On Tue, Jun 23, 2009 at 11:44:57AM -0400, Gregory Haskins wrote:
>   
>>>>  This proposed approach forces us into a
>>>> potential O(256) algorithm in the hotpath (all MMIO/PIO exits will hit
>>>> this, not just in-kernel users).  How would you address this?
>>>>     
>>>>         
>>> Two ideas that come to mind:
>>> - add addr/len fields to devices, use these to speed up lookup
>>>   
>>>       
>> Yep, thats what I was thinking as well.  We can have the top-level
>> (group) be an rbtree on addr/len, and then walk the list of items at
>> that address linearly using your read/write() approach.
>>
>>
>>     
>>> - add a small cache that can be scanned first
>>>   
>>>       
>> Yep, I think we may want to do this anyway independent of the search alg.
>>
>>     
>>> In both cases, you first do a fast lookup, ask the device whether
>>> it wants the transaction, then resort to linear scan if not
>>>   
>>>       
>> -Greg
>>
>>     
>
> Looks like we have a concensus then.
>
>   

Yep.  I'll try to go over the patch in detail today and provide any more
feedback.

Thanks Michael,
-Greg


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